Thank you Richard, your workflow is almost exactly the same I am doing.
With the help of Nyall I have been able to track down the issue to a missing package python3-pyqt6.qtmultimedia. The debugging process involved removing all the imports from https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui.sip.in and find the broken piece, to my surprise, removing the lines highlighted here https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui.sip.in#L16C1-L20C22 eventually led to a readable error message (QtMultimedia could not be imported) instead of the corrupted one. Why the error message gets corrupted after qsci is imported (or after https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui_auto.sip is imports, I don't know which one is responsible of the issue) still remains a mystery to me. Thank you all for the help! On Mon, Jul 21, 2025 at 8:23 PM Richard Duivenvoorde <[email protected]> wrote: > I'm on Trixie (next stable in a couple of weeks), and only build QWT > myself from source: > > # https://qwt.sourceforge.io/qwtinstall.html > # download the tar.bz2 from > https://sourceforge.net/projects/qwt/files/qwt/6.3.0/ > # unpack and go into ~/git/qwt-6.3.0 dir > # error: qmake: could not find a Qt installation of '' -> > https://askubuntu.com/questions/1460242/ubuntu-22-04-with-qt6-qmake-could-not-find-a-qt-installation-of > ? > qtchooser -install qt6 $(which qmake6) > export QT_SELECT=qt6 > # create Makefile > /usr/bin/qmake qwt.pro > # compile > make > # install (in /usr/local/qwt-6.3.0 ) > sudo make install > > Then, leaving out a lot of stuff...: > > mkdir buildqt6;cd buildqt6;ccmake -GNinja -DBUILD_TESTING=FALSE > -DENABLE_TESTS=OFF -DWITH_SERVER=FALSE -DWITH_3D=FALSE > -DCMAKE_INSTALL_PREFIX=/home/richard/bin/qgis_/qt6/debug > -DWITH_QWTPOLAR=OFF -DCMAKE_BUILD_TYPE=Debug -DWITH_GRASS=FALSE > -DBUILD_WITH_QT6=TRUE -DWITH_OAUTH2_PLUGIN=FALSE > -DWITH_WITH_SERVER_PLUGINS=OFF -DWITH_STAGED_PLUGINS=OFF -DWITH_PDAL=OFF > -DWITH_QTWEBKIT=OFF -DQWT_INCLUDE_DIR=/usr/local/qwt-6.3.0/include > -DQWT_LIBRARY=/usr/local/qwt-6.3.0/lib/libqwt.so .. > > in the same git repo as my qt5 build, QGIS works. > > I'm on python 3.13.5 here > > Not sure if this helps... > > Richard > > > > > On 21-07-2025 17:52, Alessandro Pasotti via QGIS-Developer wrote: > > > > Thanks, I'm using Python 3.13 (that comes with that Ubuntu version). > > > > Now I'm trying with vcpkg ... > > > > > > On Mon, Jul 21, 2025 at 5:35 PM pathmapper <[email protected] > <mailto:[email protected]>> wrote: > > > > Hi, > > > > I don't know what's wrong, but when I had similar problems, > switching to > > Python 3.12 solved them for me. > > > > Cheers, > > Björn > > > > On 21.07.2025 16:58, Alessandro Pasotti via QGIS-Developer wrote: > > > Hi, > > > > > > I am trying to build QGIS with QT6 on Ubuntu (tried 24.10 and > 25.04), > > > it builds without errors but when I run it, the following error > > > appears: > > > > > > Couldn't load PyQGIS. > > > Python support will be disabled. > > > > > > Traceback (most recent call last): > > > File "", line 1, in > > > File > > > > "/home/ale/dev/QGIS/build/Desktop_QT6-Debug/output/python/qgis/gui/__init__.py", > > > line 25, in > > > from qgis._gui import * > > > RuntimeError: qgis._gui cannot import type '���A� ' from > > > PyQt6.QtCore > > > > > > Python version: > > > 3.13.3 (main, Jun 16 2025, 18:15:32) [GCC 14.2.0] > > > > > > QGIS version: > > > 3.99.0-Master 'Master', e717e3cd2b9 > > > > > > Python path: > > > ['/home/ale/dev/QGIS/build/Desktop_QT6-Debug/output/python', > > > '/home/ale/.local/share/QGIS/QGIS3/profiles/default/python', > > > > '/home/ale/.local/share/QGIS/QGIS3/profiles/default/python/plugins', > > > > '/home/ale/dev/QGIS/build/Desktop_QT6-Debug/output/python/plugins', > > > > '/home/ale/dev/gdal/desktop-install/local/lib/python3.13/dist-packages', > > > '/home/ale/dev/gdal/autotest/pymod', '/usr/lib/python313.zip', > > > '/usr/lib/python3.13', '/usr/lib/python3.13/lib-dynload', > > > '/usr/local/lib/python3.13/dist-packages', > > > '/usr/lib/python3/dist-packages'] > > > > > > I checked the QGIS/build/Desktop_QT6-Debug/output/python/qgis > content > > > and it looks legit. > > > > > > PyQt6 installation also looks ok, importing core works ok, only > gui > > > does not work. > > > > > > Any idea about what's going wrong? > > > > > > -- > > > > > > Alessandro Pasotti > > > QCooperative: www.qcooperative.net <http://www.qcooperative.net> > [1] > > > ItOpen: www.itopen.it <http://www.itopen.it> [2] > > > > > > Links: > > > ------ > > > [1] https://www.qcooperative.net <https://www.qcooperative.net> > > > [2] http://www.itopen.it <http://www.itopen.it> > > > > > > _______________________________________________ > > > QGIS-Developer mailing list > > > [email protected] <mailto: > [email protected]> > > > List info: > https://lists.osgeo.org/mailman/listinfo/qgis-developer < > https://lists.osgeo.org/mailman/listinfo/qgis-developer> > > > Unsubscribe: > https://lists.osgeo.org/mailman/listinfo/qgis-developer < > https://lists.osgeo.org/mailman/listinfo/qgis-developer> > > > > > > > > -- > > Alessandro Pasotti > > QCooperative: www.qcooperative.net <https://www.qcooperative.net> > > ItOpen: www.itopen.it <http://www.itopen.it> > > > > _______________________________________________ > > QGIS-Developer mailing list > > [email protected] > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer > > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer > > -- Alessandro Pasotti QCooperative: www.qcooperative.net ItOpen: www.itopen.it
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